Bore sight



April 17, 1951 BROWN 2,548,851

BORE SIGHT Filed NOV- 9, 1944 2 Sheets-Sheet 1 LEE] H BREIWN,

. EWOM April 17, 1951 L. H. BROWN BORE SIGHT 2 Sheets-Sheet 2 Filed NOV. 9, 1944 mHrnm Patented Apr. 17, 1951 UNITED STATES PATENT OFFICE BORE SIGHT Leo H. Brown, Glenville, Conn. Application November 9,1944, Serial No. 562,639

a 8 Claims. (01. 3346) (Granted under the act of March 3, 1883, as

amended AprilB O, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment ,to me of any royalty thereon. V

The present invention relates to a bore sight for cannon.

Among the objects of thepresent invention is the provision of a telescopic bore sight which is free of certain inaccuracies which exist in previous telescopic bore'si'ghts which are intended to be centered in use with respect to the axis of the chamber of a cannon.

A further object of the present invention is the provision of a telescopic bore sight which may have the optical axis of its telescope canted slightly'to the axis of the bore of the cannon Without the production of substantial error in bore sighting.

Another object of the present invention is the provision of a bore sight for cannon that will give satisfactory results even though the axis of the chamber of the cannon is not a straight line continuation of the axis of the bore of the cannon. It frequently occurs either in manufacture, or because of deformations occasioned by use, that the axis of the chamber of a cannon does not coincide with the axis of the bore, and that the axis of the chamber is canted or inclined to the axis of the bore of the cannon. This cant or inclination may amount to as much as seven mils. It will, therefore, be evident that when a telescope is so disposed in such a canted chamber, that its optical axis is coincident with the axis of the chamber, the optical or principal axis of the telescope is not aligned with the axisof the bore of the cannon, but is inclinedthereto.

'Still another object of the present invention is the provision of a bore sight of the telescopic type which makesuse in boresightingtof the image of the muzzle end .of the boreformed by the objective of the telescope.

Another object of the invention consists in the provision in the telescope of a telescopic bore sight of an adjustable reticle which can be .cen-

tered, in use, with respect to the image of the muzzle end of the bore produced by the objective of the telescope.

The provision of a reticle which eliminates parallax between the image of the muzzle end of the bore and reticle markings used in connection pointed out, in the description of the inventio given below.

The accompanying drawings illustrate several embodiments of the invention. In these, drawmgs: 1

Figures 1 and 2 are schematic views illustrating how certain optical principles areapplied in the present invention.

Figur 3 illustrates in longitudinal section one form of a device according to the invention located at the position at which it may be'used in the chamber of a cannon.

Figure 4 is a section on the line 4'4 of Fig.3. Figure 5 is asection on the line 5-5 of Fig.';3. Figures 6 and '7 illustrate in longitudinalsection twoother forms of a device according to the invention located at the positions at which they may be used in the chamber of a cannon. Figure 8 is a section on the-line 18 -8 of Figure 6. Figure 9 is a section on the line 9- 9 of Figure 6.

.Figure 10 is a longitudinal sectionof, par'tfiof the telescope illustrated in Figures3, 6 and "7, showing in detail one .form of ,reticle of the telescope and its mounting. Figure 11 is asection on theline ll ll of Fig. 10. v l K Figure 12 illustrates the view. obtained through thetelescope used inthe invention, .when aQcannon is bore sighted and the. telescope reticle markings consist of a circle and cross at ,its center. .j

Figures 13.,and 14 are enlarged viewsofan engraved glass reticle plate that may beused; to

that may be used instead. ofthe-reticlesil-lustrated in Figs. 10,11,13 and-l4.

Figure 16 is a section on the line [6-46. of Fi 15.

It is an experimental fact that if a converging lens isused to form a real image of an object,

and the lens is then turned small angular amounts about axesperpendicular tothe principal axis of the lens near or at the optical center or nodal points of the lens, there will be very little, if any, displacement of the position in space of the real image'of the object. That is -;to say, the'real image remains substantially fixed in--space in spite of the said rotation of the lens about said axes.

The present invention makes use of the above scientific fact or principle in order to overcome defects in prior telescopic bore sights which attempt to center the optical axis of their telescopes with respect to the axis of the bore of the cannon by centering it with respect to the axis of the chamber of the cannon. In this description, the bore of a cannon is considered to be the inside part of the barrel that is provided with riflings. If the geometrical axis of the chamber of the cannon is centered with respect to the bore of the cannon, or constitutes a continuation of the axis of the bore, then, of course, centering the optical axis of the telescope in the chamber of the cannon, centers it with respect to the axis of the bore of the cannon. However, the geometrical axis of the chamber, is usually not a true straight line continuation of the axis of the bore, since frequently, because of faults in manufacture, or because of deformations occurring in use, the geometrical axis of the chamber of the cannon is slightly inclined or canted to the axis of the bore. As before stated, this inclination or cant may reach the extent of seven mils or more. Now, when, as has been the practice heretofore, the telescope of a telescopic bore sight is centered in a chamber whose axis is canted with respect to the axis of the bore, the optical axis of the telescope is not centered with respect to, or in alignment with, the axis of the bore of the cannon. Thus error is introduced in bore sighting when using these prior devices. The present invention overcomes this error.

The application of the above considered optical principle in the present invention will become evident upon consideration of Figures 1 and 2 of the accompanying drawings.

In said Figures 1 and 2, the numeral I indicat-es the muzzle end of a cannon; and the numeral 2 indicates a diameter of the bore at the muzzle end and also the round opening at the muzzle end. The objective of a telescope of a bore sight is indicated in the said Views by the numeral 3. The real images of the muzzle end of the bore formed by the objective lenses 3 are indicated by the numerals 4. Lines 1 and 8 indicate rays of light from the circumference of the muzzle end of the bore to the real images 4 of the said circumfer ence. Reticle or reticle plates 6 are shown in both figures somewhat displaced from the focal planes of real images 4, in order to show clearly the relative position of the reticles 6 and real images 4 formed by the objectives 3 of the telescopes. Lines AB and AC indicate respectively the axis of the bore of the cannon and the axis of the chamber at the breach end. In Figure 1, the line AC (the axis of the chamber) is centered with respect to the axis AB of the bore, that is, AC is a continuation of the straight line AB. In Figure 2, the axis AC of the chamber is shown inclined or canted (on an exaggerated scale) to the axis AB of the bore. Line AD represents a continuation of line AB.

In Figures 1 and 2, the principal axes of the objectives 3 of the telescopes coincide with the lines AC in both figures, and the reticles or reticle plates 6 are perpendicular to both of said lines as they would be in a telescope. The eyev pieces of the said telescopes have been omitted from said figures for purposes of simplicity, but they would be placed in the usual positions to view the real images 4, as shown in Figures 3, 6

and 7 hereinafter considered.

In Figure 1, the principal axis of the objective 3 coincides with the straight line CAB, but in Figure 2, the principal axis of the objective 3 coincides with the line AC (the axis of the chamber) but is inclined or canted with reference to the axis AB of the bore of the cannon. In Figure 2, the objective 3 is so positioned that the optical center or a nodal point of the objective is located or placed on or near the line AB which represents the axis of the bore of the cannon or a continuation AD of it towards the breech end of the cannon. Under these conditions, as explained above, the real image 4 of the muzzle end of the cannon is not substantially displaced or moved in space, in spite of the fact that lens 3 has been rotated relatively to the axis of the bore an angular amount corresponding to the angle DAC (which is shown much greater than it would be in actual practice, for purposes of illustration). There may be some very slight amount of blurring or distortion of the image, but its position in space from a practical point of view in practicing the present invention is substantially the same as in Figure 1.

It will be seen, therefore, from the foregoing explanations, that the center of the real image 4 of the muzzle end of the bore occupies the same position in space in the case of Figure l as in the case of Figure 2, and as a consequence, in order to bore sight, even in the case of a canted chamber, it becomes now only necessaryto center a distant target on the center of the real image 4 of the muzzle end of the cannon bore. This is done according to the present invention by providing an adjustable reticle, or reticle plate 6 with respect to which both the image 4 of the muzzle end of the bore of the gun and of the distant target sighted on in bore sighting can be centered.

To the above end, the reticle may comprise a glass reticle plate with an engraved circle reticle slightly smaller or larger than the real image 4 of the muzzle end of the bore and a small cross engraved at the center of the circle. The circle reticle may advantageously be made approximately the same diameter as the diameter of the circular real image 4 of the muzzle end of the bore. Any other suitable figure with respect to which the image 4 can be centered may be used instead of the said circle and cross, for example a regular hexagon or octagon with a cros at their centers may be used. An ordinary cross-hair reticle may be used also, provided the usual annular support therefor has an annular opening therethrough (and across which the cross hairs are stretched) which is slightly larger than the real image 4 of the muzzle end of the bore, so that the said image can be equally spaced from all part of the circular boundary of the said circular opening of the reticle support.

The specific embodiments of the inventions hereinafter described apply the above explained principles of operation.

For the purposes of brevity and simplicity oi reference and of definition in the claims, the optical center and/or nodal points of the objectives of the telescopes are bothreferred to as the center of the objectives. With this definition of terms, the families of axes perpendicular to the principal axis of the objective of the telescope and around which the objective may be rotated small angular amounts, without material or substantial displacement in space of the real images formed by the objective, intersect the principal axis of the objective at or near the center of the objective,

In .all of the embodiments of the invention hereinafter .described,.the centerof theobjective,

.thecen'ter. of the lens'lies on or.is.placed-..on or in .theaxis of: the .bore,.;all-three conditions just mentioned are included, namely the said. center ':-may. be on, substantially on orat least very near the axis of thebore of the cannon or. a. continuation of it towards the breech end of. the cannon. :Therefore, alsowhen the term. axis. of the bore of the cannon is referred to, the continuation of the .axis towards the breech end of the cannon is also included as an integralpart of the axis of the-bore.

Referring now-specifically to the embodiment v:ofthe invention illustratedin Figures 3, 4 and5, the numeral H3 designates a cannon having bore .I:l..and a chamber consisting of a rearpart l2 andfia forward part-l3. The parts [2.and I3 in .man-ufacture are made coaxial and are intended tolbezcoaxial with the bore l l. Between thefor- --ward\partl3 and the rear part 12 of the chamber is-a' shoulder I i-frequently present in can- .non. At the forward part E3 of the chamber is .forcingcone i5-marking.the.beginning of the riflingsof bore .li.

A telescope miscarried-by a cylindrical carrier I9, said telescope being mounted in a central hub-2U carried by .the rear end wa1l2l of cylindrical carrier [9. The telescope it has its optical axis coaxial with the axis. of cylindrical carrier 19. Cylindricalcarrier l9 has a close sliding fit with thecylindrical wall-of the rear-portion I2 ofthe cartridge chamber of the cannon, so that the optical .axis of the telescope.coincides,.or substantially conicides, with the geometrical axis of the rearportion -l2-of the chamber, when the telescope 18 and cylindrical carrier-l9 are insertedintothe portion l2 of the cartridge chamber as shown in Figure 3of the drawings.

Telescope It? may comprisean objective lens .-.22, erecting lenses 23, eyepiece lens 2-4, carried in adjustable eye piece'25, and-a reticle means 26 which is constructed in-accordance with the present invention, as explained hereinafter.

Reticle means 26 (see FigsI-O to. 14) may com- .prisean adjustable reticle'support 2?, and-a glass .reticleplate 23 provided withcircle reticle marking 29 and cross reticle markings-3B, both entration-in thedrawings, the circle 29 has a-diameter slightly smaller than theimage of the bore inthe plane of the circle 25, as shown in Fig-.12, wherein circle 3! indicates the outlineof the image of the opening at the muzzle of the cannon and thenumeral 32 indicates the part of the riilingsof the bore that is seen in the telescope.

.Thethickness of the plate 28, orthe distance between the plane of .circle29 andlthe plane .of cross 30,. is such thatthe image .of-a.distant target corresponding to an infinite target is brought to. said circle 29.

6 to focus in the ..plane .of the cross 39 while .the image of themuzzle .end of the bore .ofthe cannon. is brought tofocusin the plane ofthe circle 29. .This eliminates the parallax referred to.above,so .that the eye .of. the user-may .be moved laterally -during sighting without producing apparent motion between the images and reticles.

.The reticle support 2! is provided with two flat,

portions 35-(see Fig. 11) ninety degrees apart against which adjustment crews 3Bv and 31 abut.

A. leaf .-.spring 38 is attached at 39, intermediate its ends, .to reticle support 27. Reticle support 21,.carrying-the glass plate 28 and springt39, is positioned in the sleeve at between fixed rings 4! .anddzand-may slide between said rings when adjustment screws 36 and Stare turned to adjust .the position of the reticle means with reference to theoptical axis of the telescope. Thesleeve ifi'isfixedin position in the barrel of telescope -18, so that the image. of infinite target comes to focus in the plane of reticle cross that is in the plane or face of reticle. plate 28 nearer the objective lens of the telescope.

Leaf spring 538 is so shaped and positioned, as shown in .Fig. ll, that it urges reticle holder or support Z'itowards and against the .ends of adjusting screws 3% and 31. Adjustment screws 36 and 3?.are threaded through the barrel .of the telescope and sleeve it. It will be seen that screws 36 and N enable the reticle means to be adjusted inplanes at right angles to each other, whereby the center. of the circle reticle. 29 can be, positioned atany desired position with reference to the optical axis of'the telescope.

.In bore. sighting, according to the present invvention it willno-wbe understood that if the image ofthe muzzle endof the bore of the gun is not the muzzle endof the bore is centered with respect After this has been done, the cannon is elevated and/or traversed so as to bring the image of a distant point upon the crossing point of the lines of cross reticle 3U, whereupon the telescope of the cannonsight issighted upon, that .is, its reticle brought upon, the same distant point.

Another form of reticle means which maybe usedin the practice of the present invention is illustrated in Figures 15 and 16. This reticle meanscomprises a reticle support 47 having a round aperture 38, andannular flange 49, the

the latterbeing providedrwith flats 5G andil The edge of the round aperture 48 -(which is preferably in the; form of a perfect circle) isbevelled, asshown in whioh'areninety degrees apart.

Figure, 16, to .form a knife edge 52 completely around'the circle. Cross wires or filaments 53 and 54 are stretched, at right angles to each other,

across theopening 48, so that the crossing point "55 "of thecross-ing filaments or wires is at the 10 and 11) are mounted in the telescope.

In connection with the reticle means shown in Figures 15 and 16, it is to be noted that the plane of the knife edge 52 around the circular opening 453 is spacedfromthe plane of the cross-Wires 53 and 5d by the thickness of the wall of the circular opening 48. This distance 'or thickness is so chosen that the image of the muzzle end of the bore is-broughtto' focus inthe-plane of the knife 7 edge 52, whereas the image of a distant point, corresponding to infinite distance, is brought to focus in the plane of the cross-wires 53 and 54. It will, of course, be understood from earlier parts of this description, that the plane of the crosswires 53 and 54 is nearer the objective of the telescope than the plane of the knife edge 52 around the circular opening 48.

Another embodiment of the invention is illustrated in Figs. 6, 8 and 9; Parts in these figures corresponding to parts in the modification illustrated in Figures 3, 4 and are indicated by the same numeral with the letter a appended thereto. The telescope is mounted in and carried by two disks 60 and 6 l The optical axis of the telescope coincides with the axes of the two disks. The disks 6! and BI have a close sliding fit with the wall of portion [2a of the cartridge chamber, so that the assembly can be inserted in the part 120, of the chamber with the optical axis of the telescope substantially parallel with the geometrical axis of the portion 12a of the chamber of the cannon.

Still another embodiment of the invention is illustrated in Figure '7. Parts in this figure corresponding to parts in the modification illustrated in Figures 3, 4 and 5 are indicated by the same numeral with the letter b appended thereto. In thi modification, two disk 65 and 66 corresponding to disks 6!! and 6| of Fig. 6 are employed, except that the disks 65 and 55 are smaller in diameter in order to have a close sliding fit with the forward portion [3b of the cartridge chamber.

In all of the modifications of the invention the center of the objective lens of the telescope is V placed at or substantially at that part of the mounting for the telescope nearest the forcing cone of the cannon. Thus, in Fig. 3 the center of objective 22 is located at the forward part of cylinder 19, and in Figures 6 and '7, the center of objective lenses 22a and 22b are located at the forward facesof disks 6! and 66 respectively. This means that when the telescopic assembly is inserted into the cannon in the positions shown in Figures 3, 6 and '7, the centers of the objective lenses will assume a position on or substantially on the axis of the bore of the cannon, even though the optical axis of the telescope is not co-axial with the bore of the cannon because of a cant or inclination between the axis of the cartridge or propellant chamber and the axis of the bore. Thus, while the optical axis of the objective may be slightly inclined to the axis of the bore of the cannon, the images formed by the objective are not displaced in space as explained above. In use,

the reticle is moved over to where the images are located in space and the image of the muzzle end of the bore centered with respect to a reticle and thereafter the image of a distant point centered with respect to said reticle or, what amounts to the same thing, centered with respect to the image of the muzzle end of the bore.

It will therefore be seen that the present invention utilizes an image of the muzzle end of the bore of a cannon in an entirely novel manner in bore sighting cannon; that bore sighting of cannon, by means of the present invention, can be accomplished by the present invention even though the axis of the chamber of the cannon is canted or inclined to the axis of the bore of the cannon; and that parallax between the images and their respective reticles is eliminated during the bore sighting operation.

I claim:

1. In a bore sight for a gun, a telescope comwer prising an objective, a first reticle identifying a point lying on the optical axis of said telescope, and a second reticle in fixed relation with said first reticle and spaced therefrom; said second reticle defining a closed line symmetrical about said optical axis, and means connected with said telescope and engaging said gun, said means being adapted positively to locate said telescope at the breech end of said gun, with its optical axis substantially coincident with the axis of said bore, and with said objective in position to focus an image of the muzzle end of said bore in the plane of said second reticle while simultaneously focusing the image of an aiming point, located at infinity, in the plane of said first reticle.

2. A bore sight for cannon having a bore enlarged at its breech end to form a cylindrical chamber for propellant supposedly coaxial with said bore, a, telescope frame, a first reticle in said frame having points defining a circle adapted to be arranged concentrically with an image of the muzzle end of said bore, a second reticle in said frame spaced forwardly of said first reticle and adapted to lie on and identify a point on the bore axis of said gun, an objective in said frame, and means positively locating said frame, reticles and objective within said chamber so that said objective focuses the muzzle portion of the bore of said cannon in the plane of said first reticle while focusing an aiming point located at infinity in the plane of said second reticle.

3. In a bore sight for a gun, a telescope comprising an objective and a fiat pane of transparent material spaced from said objective along the optical axis of said telescope, there being a first reticle on the objective side of said pane defining a point on said optical axis and a second reticle on the opposite side of said pane defining a circle concentric of said axis, and means fixed with said telescope and adapted positively to locate and support said telescope within the breech portion of said gun with its optical axis substantially coincident with the axis of the bore thereof, said objective, pane and gun being then so related that said objective focuses an image of the muzzle portion of the-bore of said gun in the plane of said second reticle while simultaneously focusing the image of an aiming point at infinity, in the plane of said first reticle.

4. A bore sight as recited in claim 3, and means mounting said pane in said telescope for universal translation in the plane thereof and transversely across said optical axis.

5. In a bore sight for a gun having a bore enlarged at its breech end to form a cylindrical chamber substantially coaxial with said bore, a

telescope comprising an objective, a first reticle identifying a point on the optical axis of said telescope, a second reticle spaced from said first reticle and comprising a closed line symmetrical about said axis, means adapted to positively locate said telescope within said chamber with its optical axis substantially coincident with the axis of said chamber and with said objective substantially at the junction of said bore and chamber, said objective and reticles being so spaced that, when said objective is located as aforesaid, an image of the muzzle end of said bore is focused in the plane of said second reticle while the image of a target at infinity and lying on said bore axis, is focused in the plane of said first reticle and means mounting said reticles within said telescopes for conjoint translation transversely across the optical axis thereof.

6. In a bore sight for cannon, a telescope provided with an objective and a reticle adjustable in a plane substantially perpendicular to the optical axis of said telescope, said reticle comprising a circle with respect to which the image of the muzzle end of the bore may be centered, and reticle means indicating the center of said circle, and means positively mounting and locating said telescope within the breech chamber of said cannon with said objective substantially centered on the axis of the bore of said cannon and in the plane of the forcing cone thereof.

'1. In a bore sight for a cannon having a bore surface, and a breech chamber surface supposedly, but not necessarily, coaxial with the bore surface, a telescope comprising an objective, an eyepiece, a reticle, means mounting said reticle at the focal plane of said objective and eyepiece, for limited translation only in said plane, and means connected with said telescope and adapted to be supported by and to cooperate with the breech chamber surface only, to positively position said telescope with its principal axis coincident with the axis of said breech chamber surface and with its objective on the axis of the bore surface of the cannon and substantially in a plane transverse of the cannon between said surfaces, said reticle comprising a circle of a diameter substantially equal to the diameter of the image of the muzzle of the cannon projected thereon by said objective.

8. In a bore sight for a gun having a bore enlarged at its breech end to form a breech chamber having an axis intersecting, but not necessarily coincident with the axis of the bore surface, a telescope including a tube, an objective and a reticle in said tube, means mounting said reticle in the focal plane of said objective for universal translation in said plane across the principal axis of said telescope, and means attached to said telescope and engaging the walls of said chamber positively to locate and support said telescope with its principal axis coincident with the axis of said chamber and with the center of said objective at a point determined by the intersection of the axis of the bore of the gun with a transverse plane between said bore and chamber, said reticle comprising a regular geometrical figure of substantially the same size as the image of the muzzle of the gun projected upon said reticle by said objective.

' LEO H. BROWN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

